When your housemate get steaming drunk and comes home in the early hours of the morning and despite having keys in their pocket, they deem it necessary to defecate on the dividing wall between ones house and the neighbours.

As an act of tagging, the culprit leaves a momento such as a wallet at the scene.

Ben came home late last night
How was his night?
He took a shit on the wall
How did you know it was him?
He left his calling card